The invention relates to a lower thread tension adjusting device used in combination with a sewing machine.
In a stitching operation by a sewing machine, it is generally required to adjust the tension of a lower thread in dependence upon a kind and/or thickness of the fabric to be sewn as well as types of stitches. This has been attained in such manner that the lower thread is adjustably pressed against an abutment by a leaf spring which is subjected to manipulation of an adjusting screw by a machine operator. This tension adjustment, however, has been carried out by guesswork with no reference and therefore can not easily be done by an unskilled operator.